Telephone system



Feb. 13, 1940. s. c. REIER TELEPHONE SYSTEM Filed May 21, 1938 G. C. RE/ER BY A TTORNEV E .356 M .i 1 Q3 5 III.IJIIIJHJ| m I V 2 W NW ON! \N .u k: n: I.- \N Qua: mm mukan mm 2 I E QQ mm: 593a Nn Patented Feb. 13, 1940 srarss areur OFFICE TELEPHONE SYSTEM fi George C. Reie r, Wcstfield, N. J., assignor to Bell Telephone Laboratories, Incorporated,

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i This invention relatesflto telephone conference systems and particularly to an improved method of connecting a plurality of multiparty lines with a master station for conference purposes. It is the object of this invention to increase the station capacity of telephone conference systems of the type which utilizes a bridge type transformer or-hybrid coil as the connecting medium. between a master station equipped with loud-speaking l receiver and distant talking transmitter, and

groups of subordinate stations which normally have access to andlare accessible from a central ofice. ;i I l t This object is attained in accordance with a 515 feature of the invention by utilizing both ends of F2 hybrid coil for speech'transmission purposes thereby substantially-doubling the station capacity oi. such systems wherein but one end of I the coil is "used for the transmission of speech and 550 the other is connected to a balancing network.

Another feature of the invention resides in maintaining a normal condition of balance betweenthe speech transmission channels consti tubing the conference circuit and inproviding .2 means for associating any number of stations with their respective speech channels without dis- Hturbing the normal condition of balance. More,

specifically each branch of the conference circuit, or each speech channel extending from the "30 hybrid coil, has normally connected thereacross plurality of impedance networks which correin number to the number of stations having nesting from the conference circuit 2. corresponding impedance network. I i

These and other featuresof the invention will readily understood from the following detailed description made with reference to the accomying drawing in which the single figure illus- 3323a, features of the invention.

i In the rectangleMshown at the left centre of .quipm ent comprises a hybrid coil or bridge type transformer M of the well-known three l wi "ng type. Across the input winding of this coil there is connected the output terminals of an 55 amplifier [2 whose input terminals are permai a balancing network 213.

23 of switch 2i.

a conference arrangement embodying the t e drawing there included the telephone equipwhich is located at the master station.

nently connected to a distant talking transmitter 3. The windings i3 and Hot the hybrid coil iii are herein designated first and second line windings since the usual nomenclature applied to these windings, namely lineand network windings =5 does not apply in thepresent arrangement. The line terminals of the'windin'g l3 are permanently connected to the line wires lS'and i 6 'of one of the speech channels L whereasthe line terminals of the winding M are permanently connected to the line wires i3 and 18 of the second speech channel L1; Across the mid-points of coils l3 and I l a loud-speaking receiver Bis connected by way of an amplifier 8. Battery supply for the, telephone stationsmay be provided from a com:- mon source 39 throughthewindings of impedance coil M as shown; or by means of individual battery supply arrangement-aim each station. Battery supply for the distant talking transmit ter, #3 may be supplied in any well-known manner. 29

At A there is shown a subscribers station which includes the usual subset equipment as generally indicated at 20, a manually operable key 21 and As illustrated, the balancing network 22 is normally bridged across the .25 line wires 55 and [6 of the conference branch, or speech channel L by way of the normal contacts The substation equipmenttfl is normally connected to the central ofiice line wires 2t and 25 byway of the normal contacts 26 and 39 2! of switch 2i, Under normal condition of the switch 2! the balancing network 22 is bridged across the conference channel I.- and the subscribers set 36 is connected to the central office line comprising conductors 24 and 25. It is to be understood that the impedance of network 22 equals the impedance of the subset 20. When 'the key 24 is actuated, contacts23 and 26 and 21 are opened so that the network 22 is disconnected from the conference channel L and the subset 40 2c is disconnected from its individual central office line circuitl Contacts 25 and 29 are closed by the actuation of switch 2! thereby causing the sub-set 2%) to beconnected to the speech channel L.

The hybrid coil Hi serves to connect the transmittiug and receivingcircuits at the master station in conjugate relation whilepcrmitting transmissionfrom the transmitter Hi to both conference branches L and L1. It also allows transmission from both branches L and L1 to the loudspeaking receiver 9 while maintaining said branches in conjugate relation to one another.

The equipment atstations B, C and D is identia cal with that of station A and no further description thereof is deemed necessary. It will be understood that the balancing networks at each station must have the same impedance as the subset which replaces it when the corresponding key such as 2| is actuated. All of the subsets need not have identical impedance frequency characteristics but each set in branch L however, must have a similar set in branch L1.

Any suitable method may be employed for signaling between stations. A simple arrangement may comprise a buzzer 32 located at each station and a key 4!] at the main station, the latter when operated causing the energization of all station buzzers of the system. It is not necessary that the main station be provided with a buzzer signal since the subscriber 'thereat may be signaled from another station by the subscriber thereat speaking into his transmitter after the actuation of his key 2|. Code signaling would,

of course, be resorted to so that each station of the system may be signaled and the subscriber thereat recognize that the call is intended for him.

In the following description it' will be assumed that the subscriber at the master station M desires to summon the subscribers at stations A, B, C and D for conference purposes. The key 40 at the master station would be actuated causing the operation of all the buzzers 32 located at the stations A, B, C and D. A particular code may be employed to indicate that the subscribers are being called for conference purposes. Upon re- 'ceipt of such a signal the subscriber at each station throws his respective switch 2! to its operated position and removes his receiver from its switchhook thereby placing the system in readiness for the transmission of speech. It will be understood that regardless of how many of the subscribers at the stations A, B, C and D respond to the signal, the normal balance of the system is not disturbed since at each station there is normally connected to the conference channels a network having an impedance frequency characteristic similar to that of the associated subset and the substitution of one impedance for a similar one will not affect the impedance of the entire system.

Speech currents generated when the distant talking transmitter it at station M is agitated will divide equally between the line coils l3 and Hi and will be transmitted over the speech channels L and L1 to energize those receivers at statio-ns A, B, C and D which are now connected to their respective speech channels L and L1. Speech currents generated at the transmitters of the various stations A, B, C and D will pass through the hybrid coil windings l3 and M and activate the loud-speaking receiver 9 by Way of the amplifier 8. In this manner two-way conversation may be carried on between the master station and the several stations connected to the branches L and L1. Since with this arrangement the impedances connected to the line branches L and L1 of the hybrid coil will be practically identical, the voltages impressed on the loud-speaking receiver 9 will be substantially nil when the distant'talking transmitter i3 is agitated. It is, therefore, possible to obtain satisfactory volume from the loud-speaker without setting up a singing condition over the electrical circuit from the transmitter to the receiver and the acoustic path from the loud-speaker to the distant talking transmitter. The advantage of the disclosed arrangement is that for a given desired transmission level from and to the master station twice as many telephone stations can be included in the conference as could be used if the sets were all connected to one line winding of the hybrid coil and balancing networks to the other line winding.

Sufiiciently good transmission from the telephone sets A and B in branch L of the hybrid coil to telephone sets C and D in branch L1, or vice versa, will be obtained through the acoustic path between the loud-speaking receiver and the distant talking transmitter at the master station to permit conversation between stations in different branches. r

As illustrated in the drawing each substation A, B, C and D is normally connected to a central ofiice line so that the subscribers at these stations may be signaled from the central oflice and may initiate outside or central office calls in the usual manner.

What is claimed is:

1. In a telephone conference system, a master station having a distant talking transmitter and a loud-speaking receiver, a hybrid coil interconnecting said transmitter and receiver in conjugate relation and having twopairs of line windings, a speech channel connected to each pair of line windings, an impedance network normally connected across each of said speech channels, a telephone set for each of said speech channels normally disconnected therefrom, and means for connecting said telephone sets to their respective speech channels and disconnecting said impedance networks therefrom.

2. In a telephone conference system, a master station having a distant talking transmitter and a loud-speaking receiver, a hybrid coil interconnecting said transmitter and receiver in conjugate relation, a pair of line windings for said coil, a second pair of line windings for said coil, a speech channel connected to each of said pairs of line windings and each having a plurality of impedance networks normally associated therewith, a telephone set for each of said impedance networks and having an impedance frequency characteristic identical to its respective impedance network, and switching means for selectively disconnecting said networks from their respective speech channels and connecting thereto their corresponding telephone sets.

3. In a telephone conference system, a master station having a distant talking transmitter and a loud-speaking receiver, a hybrid coil interconnecting said transmitter and receiver in conjugate relation, a speech channel connected to each pair of line terminals of said coil, a plurality of networks normally connected to each of said speech channels and having impedance values such that a condition of balance is maintained between said channels, a telephone set for each of said networks and having an impedance characteristic corresponding to that of its respective network, and switching means for substituting any of saidtelephone sets for its corresponding network in said speech channels.

4. In a telephone system, a central ofiice line, a subscriber's station for said line having a telephone set normally connected to said line, a master station, a speech channel, a network having an impedance identical to that of said telephone set, a hybrid coil associated with said master station and having a pair of line terminals permanently connected to said speech channel, and switching means at said subscribers station for transferring the telephone set thereat from said lineto said speech channel and disconnecting ill said network from channel.

5. In a telephone system, a plurality of central oflice lines, a subscribers station for each of said lines having a telephone set normally associated with its respective line, a master station, a speech channel, impedance networks corresponding in number to the number of said subscribers stations normally connected to said speech channel, a hybrid coil interconnecting said master station and said speech channel, and means at each station for transferring the telephone set thereat from its respective central office line to said speech channel and disconnecting a corresponding impedance network from said speech channel.

6. In a telephone system, a plurality of central office lines, a subscribers station for each of said lines having a telephone set normally connected to a particular line, a master station, a pair of normally balanced speech channels constituting a conference circuit, means comprising a hybrid coil interconnecting said master station with said speech channels, and means at each of said subscribers stations for disconnecting the telephone set thereat from its respective central oflice line and connecting it to one of said speech channels. 1

7. In a telephone system, a plurality of central office lines, a subscribers station for each of said lines having a telephone set normally connected to a particular line, a master station including a loud-speaking receiver and a distant talking transmitter, a pair of speech channels, a hybrid coil associated with the telephone equipment at said master station and having first and second line windings permanently connected to said speech channels, and means ateach of said subscribers stations for disconnecting the tele-,

phone set thereat from its respective central ofiice line and connecting it to one of said speech channels.

8. In a telephone system, a plurality of central office lines, a subscribers station for each said speech telephone set thereat from its respective central oflice line to one of said speech channels and disconnecting one of said impedance networks therefrom.

9. A loud-speaking telephone conference system comprising a pair of speech channels interconnected in conjugate relation by means of a hybrid coil each pair of whose line windings terminates one of said speech channels, a plurality of impedance networks removably connected to each of said speech channels, the total impedance of the networks connected to one of said channels equaling the total impedance of the networks connected to the other of said channels, a subscribers telephone subset for each of said networksand having an impedance equal to the impedance of its corresponding network, switching meansfor each of said networks and its corresponding subset which when operated, l

GEORGE C. REIER. 

